Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754055Ab0HZPOn (ORCPT ); Thu, 26 Aug 2010 11:14:43 -0400 Received: from gir.skynet.ie ([193.1.99.77]:45011 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753965Ab0HZPOT (ORCPT ); Thu, 26 Aug 2010 11:14:19 -0400 From: Mel Gorman To: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Cc: Mel Gorman , Andrew Morton , Christian Ehrhardt , Johannes Weiner , Wu Fengguang , Jan Kara , linux-kernel@vger.kernel.org Subject: [PATCH 3/3] writeback: Do not congestion sleep when there are no congested BDIs Date: Thu, 26 Aug 2010 16:14:16 +0100 Message-Id: <1282835656-5638-4-git-send-email-mel@csn.ul.ie> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1282835656-5638-1-git-send-email-mel@csn.ul.ie> References: <1282835656-5638-1-git-send-email-mel@csn.ul.ie> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2254 Lines: 59 If congestion_wait() is called with no BDIs congested, the caller will sleep for the full timeout and this is an unnecessary sleep. This patch checks if there are BDIs congested. If so, it goes to sleep as normal. If not, it calls cond_resched() to ensure the caller is not hogging the CPU longer than its quota but otherwise will not sleep. This is aimed at reducing some of the major desktop stalls reported during IO. For example, while kswapd is operating, it calls congestion_wait() but it could just have been reclaiming clean page cache pages with no congestion. Without this patch, it would sleep for a full timeout but after this patch, it'll just call schedule() if it has been on the CPU too long. Similar logic applies to direct reclaimers that are not making enough progress. Signed-off-by: Mel Gorman --- mm/backing-dev.c | 20 ++++++++++++++------ 1 files changed, 14 insertions(+), 6 deletions(-) diff --git a/mm/backing-dev.c b/mm/backing-dev.c index a49167f..6abe860 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -767,13 +767,21 @@ long congestion_wait(int sync, long timeout) DEFINE_WAIT(wait); wait_queue_head_t *wqh = &congestion_wqh[sync]; - /* Check if this call to congestion_wait was necessary */ - if (atomic_read(&nr_bdi_congested[sync]) == 0) + /* + * If there is no congestion, there is no point sleeping on the queue. + * This call was unecessary but in case we are spinning due to a bad + * caller, at least call cond_reched() and sleep if our CPU quota + * has expired + */ + if (atomic_read(&nr_bdi_congested[sync]) == 0) { unnecessary = true; - - prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); - ret = io_schedule_timeout(timeout); - finish_wait(wqh, &wait); + cond_resched(); + ret = 0; + } else { + prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); + ret = io_schedule_timeout(timeout); + finish_wait(wqh, &wait); + } trace_writeback_congest_waited(jiffies_to_usecs(jiffies - start), unnecessary); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/